[Tarantool-patches] [PATCH v4 3/4] memtx: allow quota overuse for truncation and deletion

[Ilya Kosarev <i.kosarev@tarantool.org>]

Trying to perform space:truncate() and space:delete() while reaching
memtx_memory limit we could experience slab allocator failure. This
behavior seems to be quite surprising for users. Now we are allowing
to overuse memtx quota if needed for truncation or deletion, using flag
in struct quota. After performing truncation or deletion we reset the
flag so that quota can't be overused any more.

Closes #3807
---
 src/box/box.cc        | 27 ++++++++++++++++++++++++++-
 src/box/memtx_space.c | 18 ++++++++++++++----
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index 1b2b27d61..1a63f25a2 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -1321,9 +1321,34 @@ space_truncate(struct space *space)
 	ops_buf_end = mp_encode_uint(ops_buf_end, 1);
 	assert(ops_buf_end < buf + buf_size);
 
+	struct txn *txn = NULL;
+	struct txn_savepoint *txn_svp = NULL;
+	if (!box_txn()) {
+		txn = txn_begin();
+		if (txn == NULL)
+			diag_raise();
+	} else {
+		txn_svp = box_txn_savepoint();
+		if (txn_svp == NULL)
+			diag_raise();
+	}
+	struct space *truncate_space = space_cache_find_xc(BOX_TRUNCATE_ID);
+	quota_on_off(&((struct memtx_engine *)truncate_space->engine)->quota, false);
 	if (box_upsert(BOX_TRUNCATE_ID, 0, tuple_buf, tuple_buf_end,
-		       ops_buf, ops_buf_end, 0, NULL) != 0)
+		       ops_buf, ops_buf_end, 0, NULL) != 0) {
+		quota_on_off(&((struct memtx_engine *)truncate_space->engine)->quota, true);
+		if (txn != NULL)
+			txn_rollback(txn);
+		else
+			box_txn_rollback_to_savepoint(txn_svp);
+		fiber_gc();
 		diag_raise();
+	}
+	quota_on_off(&((struct memtx_engine *)truncate_space->engine)->quota, true);
+	if (txn != NULL && txn_commit(txn) != 0) {
+		fiber_gc();
+		diag_raise();
+	}
 }
 
 int
diff --git a/src/box/memtx_space.c b/src/box/memtx_space.c
index 6ef84e045..3542450f7 100644
--- a/src/box/memtx_space.c
+++ b/src/box/memtx_space.c
@@ -28,6 +28,7 @@
  * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+#include "exception.h"
 #include "memtx_space.h"
 #include "space.h"
 #include "iproto_constants.h"
@@ -354,10 +355,19 @@ memtx_space_execute_delete(struct space *space, struct txn *txn,
 	struct tuple *old_tuple;
 	if (index_get(pk, key, part_count, &old_tuple) != 0)
 		return -1;
-	if (old_tuple != NULL &&
-	    memtx_space->replace(space, old_tuple, NULL,
-				 DUP_REPLACE_OR_INSERT, &stmt->old_tuple) != 0)
-		return -1;
+	if (old_tuple != NULL) {
+		bool oom = !diag_is_empty(diag_get()) &&
+			   diag_last_error(diag_get())->type == &type_OutOfMemory;
+		if (oom)
+			quota_on_off(&((struct memtx_engine *)space->engine)->quota, false);
+		int rc = memtx_space->replace(space, old_tuple, NULL,
+					      DUP_REPLACE_OR_INSERT,
+					      &stmt->old_tuple);
+		if (oom)
+			quota_on_off(&((struct memtx_engine *)space->engine)->quota, true);
+		if (rc != 0)
+			return -1;
+	}
 	stmt->engine_savepoint = stmt;
 	*result = stmt->old_tuple;
 	return 0;
-- 
2.17.1